Fibrous protein materials

ABSTRACT

Disclosed is a method for producing fibrous protein materials useful for fish analogs. According to this method, an aqueous mixture of a heat coagulable protein is frozen by cooling the mixture in a manner and at a rate effective to produce elongated ice crystals generally aligned perpendicular to the surface of cooling, then subjected to a temperature substantially different from that of the frozen mass, and the protein in the frozen mass is then stabilized effectively to preserve its structural integrity during subsequent heating to set the protein.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of prior filed copendingApplication Ser. No. 480,987, filed June 18, 1974 now U.S. Pat. No.4,001,459.

This invention relates to textured proteins. More specifically, thepresent invention provides a new process for preparing fibrous proteinmaterials which can be used as, or in the production of, fish analogs.

In recent years, considerable research efforts have been focused upondeveloping new technology for producing meat-like, protein-containingfoods from various vegetable and animal protein sources. Economicsprovides a major incentive. It would clearly be advantageous tosubstitute, at least in part, the more efficient process of growingvegetable protein for the rather inefficient process by which animalsconvert the proteinaceous vegetable materials into meat. This isespecially true where the ever-increasing human population is feared tobe out-distancing the availability of grazing land for meat-producinganimals. Additionally, recent efforts have also been directed toavoiding certain natural products which may be undesirable for religous,ethnic, or health reasons.

All natural meats, including fish and poultry, have fibrous structures.The texture of the meat products is inherently dependent upon thefibrous nature of the meat. Likewise, the presence of a fibrousstructure is an important factor in fabricated meat-like products. Thus,in producing these meat-like products, e.g. meat analogs, much efforthas been directed to creating a fibrous structure, similar to naturalmeat. Many workers have developed a wide variety of techniques forobtaining fibrocity, and a good deal of published literature isavailable on the production of meat analogs with fibrous structures.

One early worker, Boyer, in U.S. Pat. No. 2,682,466 disclosed theformation of synthetic meat products containing quantities of vegetableprotein filaments. These protein filaments are made by forcing acolloidal protein dispersion through a porous membrane, such as aspinnerette, into a coagulating bath causing precipitation of theprotein in filament form. The filaments are assembled into a meat-likeproduct by employing binding materials, including cereals and protein.The use of spun vegetable fibers enables the formation of a highlyaligned fibrous structure. Unfortunately, the manufacture of spun fibersis complicated and relatively high in cost. Moreover, spun vegetableprotein is generally poor nutritionally because the starting materialdepends on soy isolate.

In view of the difficulties inherent in spun fiber technology, otherworkers were encouraged to seek alternatives to this technique. Onealternative, disclosed in U.S. Pat. No. 3,488,770, describes theproduction of a proteinaceous meat-like product having an open celledstructure with cell length greater than cell width, and with the cellsbeing substantially aligned. This product is made by extruding a dough,substantially free of non-proteinaceous filler, into an area of reducedpressure to cause expansion. Another alternative process working with adough is disclosed in U.S. Pat. No. 3,693,533. According to thatprocess, the protein containing dough is coagulated while being passedthrough a set of converging conveyors. The resulting stretching duringcoagulation produces what are described as unidirectional fibers. Whilethese processes are potentially less costly than the spun fibertechnology, they suffer a penalty in the quality of the fibers produced.

Several workers, in Japanese Specifications 48-21,502 and 48-34,228, andUnited States Pat. Nos. 3,870,808 and 3,920,853 describe the productionof fibrous protein masses by processing including freezing a proteinsolution or dispersion and heating the frozen mass to heat set theprotein. These fibrous products are described as being meat-like. Also,applicants' copending Application Ser. No. 480,987 describes and claimssuch a process where improved products are obtained due to theemployment of a freeze drying step prior to heat setting.

Even taking the best of these teachings, however, the art has yet toclosely reproduce the type of fibers normally present in fish meats suchas tuna. The fish fibers are well ordered, but generally flake-like.This type of texture is highly desirable when trying to simulate naturalfish meat.

SUMMARY OF THE INVENTION

In view of difficulties with prior art techniques, it would beadvantageous to have a method which would be capable of producing atextured protein material having a highly-defined, fish-like fibrousstructure which would be both nutritious and economical.

Accordingly, it is an object of the present invention to provide asimple and economical method for producing a high quality texturedprotein material having a highly-defined, fish-like fibrous structure,high nutrition, excellent rehydration characteristics and good overalltexture.

These and other objects are accomplished according to the presentinvention which provides a method for producing fibrous, fish-likeprotein materials. This method, in its broad aspects, comprises freezingan aqueous mixture of heat coagulable protein by cooling in a manner andat a rate effective to create elongated ice crystals generally alignedperpendicular to the surface of cooling, subjecting the frozen mass to atemperature substantially different than that of the frozen mass tocause a temperature stress in the material at lines of weakness in thefrozen mass perpendicular to the aligned ice crystals, stabilizing theprotein in the frozen mass effectively to prevent loss of fibrousstructure during heating, and heating the stabilized material tocoagulate the protein.

DETAILED DESCRIPTION

According to the present invention, a wide variety of fish-like texturescan be simulated using a wide variety of protein materials. The commoncharacteristic of all of these products is the presence of well-defined,well-ordered fibers separated by lines of cleavage generallyperpendicular to the direction of alignment of the fibers. The fibersare produced by the present method from protein of vegetable or animalorigin--used separately or in combination. In this manner it is possibleto easily balance the textural, taste and nutritional characteristics ofthe fibers to provide a textured protein material having the desiredcharacteristics. Among the features important to the present inventionare: the need for cooling in a direction and at a rate effective toproduce the well-defined, well-ordered ice crystals; the need for ashock temperature stressing step to produce the lines of cleavageperpendicular to the orientation of the fibers; and the need tostabilize the protein prior to heat setting.

Any edible protein, or combination of proteins, can be employed in theprocess of the present invention, providing that the sole protein or, inthe case of combinations, at least one of the proteins is soluble orpartially soluble and can be stabilized by treatment according to thisinvention. In general, proteins having excellent solubility provideexcellent, distinct fibrous structures -- probably because the icecrystals can grow freely, unrestricted by undissolved solids. However,protein solutions containing considerable insoluble material, such assoy flour, meat homogenates, and fish homogenates, can also be employedwith good results to form fibrous structures according to the presentinvention. Representative of the protein materials which can be employedto give excellent results according to the present process are soy milk,soy isolates, whole milk, meat slurries, fish slurries, gluten, soyflour, wheat protein concentrate, milk whey, egg protein, blood protein,single cell protein and the like.

The final texture of the products depends in part on the protein sourceemployed, as well as the additives such as flavoring, fillers, fat,carbohydrates, salts, and the like. For example, the products preparedfrom soy milk have a juicy, smooth, soft texture with good fiber tensilestrength. The soy milk produces a product having a desirable smoothnessand softness, probably due to the oil emulsified in the protein. Soyflour, on the other hand, gives a product with lower tensile strengththan the soy milk, but this type of tenderness is desired in someproducts either alone or as a component with another protein material.

The protein, from whatever source, is admixed with water to form anaqueous protein mixture wherein at least a portion of the protein isdissolved in the water. The aqueous protein mixture can be characterizedas a solution, dispersion or suspension of protein and water. Toincrease the degree of solubility of the protein, which varies fordifferent types of protein, the pH of the mixture can be adjusted. Toobtain the optimum tensile strength and fiber integrity it is usuallydesirable to adjust the pH of the aqueous protein mixture to the pointof maximum protein solubility. The pH of the mixture appears to directlyaffect the tensile strength of the final textured product. Some proteinmaterials such as soy flour, give better texture and tensile strength athigh pH, e.g. pH 10, than at lower pH. This is probably because theseproteins are more soluble at higher pH, and are partially dissociatedand denatured by the alkaline condition before texturization. At highpH, the protein molecules tend to unfold, allowing more completedissociation and apparently allowing more freedom of movement duringfreezing to form more perfect fibers. Some proteins, such as egg white,have good solubility at their natural pH and need not have their pHadjusted to alkaline condition.

While high pH is sometimes useful in preparing the textured product,excessively high pH values are not generally desirable. The pH of thefinal product can be reduced during rehydration, to be later explainedin detail, by the use of an acid in the rehydration bath. At times,however, reducing the pH of the textured product to a level below thepoint at which the particular protein is immobilized, may affect thetexture of the product. Depending on the particular end usecontemplated, this textural effect may be desirable or undesirable. Forthe proteins which are solubilized at their natural pH of 6 to 8, noneturalization will be needed.

The aqueous protein mixture is easily obtained by mixing the protein inwater. If necessary, the protein material can be finely divided orcomminuted either before or after mixing with the water; and, the pH canbe adjusted to obtain the optimum solubility. The presence of solubleand insoluble non-coagulating materials is acceptable, and indeed insome cases desirable so long as it does not adversely affect thedesirable qualities of the fiber structure for a particular application.In some cases, the presence of excessive amounts of fat would beundesirable where it would reduce the tensile properties of the fibers.However, in other cases, a reduced tensile strength would be desirableas it would impart a more tender texture to the product. Thus, thoseadditives normally employed in forming fibrous meat analog products canbe employed according to the present invention, it being realized thatthe process of the present invention provides a process capable ofwidely modifying the compositional features of the fiber formingmaterial to obtain a wide variety of textural and nutritional variationsfrom the single basic process. It is an added advantage of the presentinvention that relatively high fat contents can be employed and a goodfiber structure obtained.

The solids concentration of the mixture can affect both product textureand processing efficiency. It is generally desirable to maintain lowsolids concentrations. One reason is that there is a tendency todiminish the distinct fibrous structure by increasing the concentrationof solids. Typically, the solids will not exceed about 40%, andpreferably not more than about 35% of the mixture on a weight basis.When the solids concentration increases, the efficiency of thestabilizing treatment is decreased. However, processing at excessivelylow concentrations loses economy due to the increased costs of removingthe water. The costs for energy, vessels, transfer and storage equipmentincrease rapidly as concentration is reduced. However, the quality ofthe fibers produced at low concentrations is high. It is thereforenecessary to determine the optimum concentration for each particularsystem, understanding that there are many influences which must beconsidered. In a very broad sense it can be said that the optimumconcentration for freezing will be anywhere from 3% to about 35%protein, with concentrations of from 10 to 30% being preferred, basedupon the total weight of the aqueous protein mixture. It is clearhowever that the optima for particular protein and additive materials,may vary widely within this range and at times extend beyond this range.

Those skilled in the art will be able to determine the optima for theparticular systems employed, especially with a knowledge of theeconomics of their particular processing equipment and procedures.Reference to the examples below will provide those skilled in the artwith working examples of a number of different systems. Anyconcentration effective to produce substantially independent, orientedfibers is acceptable according to the present invention. The particularconcentration must be determined in each case for the balance of productphysical properties and processing efficiency which is desirable andjustified. It is noted that a gelled protein material of the typeemployed in forming Tofu, where the water is restricted from forminglong crystals by the gel structure, cannot be employed according to thepresent invention.

Once prepared, the aqeuous protein mixture is frozen by coolingaccording to a defined directional pattern to provide a well-defined,well-ordered fibrous structure produced by the ice crystals. As thewater is frozen to ice crystals, the remaining protein mixture becomesmore concentrated. The formation of the ice crystals separates theprotein material into distinct, generally parallel aligned zones. Anymeans capable of accomplishing this result is suitable according to thepresent invention. The ice crystals form in a latice-work entrappingprotein in orderly fiber-like portions between the elongated icecrystals. The zones of protein material are separated from each otheralmost completely -- forming substantially independent fibers of proteinwhen coagulated. However, the zones of protein are not completelyindependent of each other and are joined at sufficient locations to bindthe individual zones into a branched or cross-linked structure. Thedegree of binding achieved is just sufficient to provide a cohesivenessto the final product similar to cooked meat, and does not destroy thesubstantially independent fibers. This binding, achieved during theformation of the fibers, eliminates the need for added binder materials.

Freezing is obtainable by cooling at least one surface, preferably onesurface or two opposed surfaces, of the mixture to below the freezingtemperature of the mixture. The cooling or refrigerating preferablycauses freezing to take place throughout the thickness of the mass toproduce generally parallel fibers, aligned generally perpendicularly tothe cooling surfaces. Desirably, the cooling surface or surfaces will beplanar; however, they can have any other, regular or irregularconfiguration. For example, a single cooling surface can be employedhaving a hemispherical, spherical or cylindrical configuration incontact with the aqueous protein mixture. In these exemplary situations,the ice crystals, and thus the protein fibers, would form generallyperpendicularly to tangents to the surface, radiating generally towardthe center. During freezing, a boundary between the frozen mixture andthe liquid mixture appears and moves in the direction of cooling. Attypical freezing temperatures employed according to the presentinvention, and where the cooling surface is not highly irregular, theboundary will generally conform to the shape of the cooled surface ofthe protein mixture. However, under other conditions according to thepresent invention, the boundary will assume a somewhat modified shape.It is to be understood that after an initial thickness of the mixturehas been frozen, the moving boundary of freezing becomes the coolingsurface through which heat transfer takes place. It is this movingboundary, which then controls the pattern of the formation of icecrystals and, therefore, fibers. The important consideration in allcases is the production of well-defined fibers having an orderlyalignment similar to natural meat. If needed, the surfaces of the massnot in contact with the cooling source can be insulated to reduce heattransfer at these surfaces. It is observed, in most cases, that thesurfaces not in contact with the one or the two opposed cooling surfacesexhibit a thickness of somewhat randomly oriented fibers. This isbecause directional cooling at these edges is difficult to obtain due toheat transfer with external sources. This edge portion can be eitherretained in the final product or severed therefrom such as by cuttingwith a knife, heated wire or the like. It is also noted that wherecooling is effected from two opposed surfaces, horizontal surfaces ofdiscontinuity appear, bisecting the thickness of the frozen mass. Thisis apparently due to the independent crystal growth from each of theopposed surfaces toward a plane of contact in the middle of the mass.

Many cooling sources can be employed according to the present invention.For example, the aqueous protein mixture can simply be placed in a panand the pan set on a piece of dry ice or submerged to a slight depth(e.g. one-eighth inch) in a cold liquid such as liquid nitrogen,ethylene glycol, brine, or the like. Alternatively, a container of theaqueous protein material can be placed on a plate freezer or between twoopposed plate freezers. Also suitable would be a moving belt typefreezer of the kind illustrated in U.S. Pat. Nos. 3,253,420 and3,606,763. The temperature employed can be any temperature effective toyield substantially independent, aligned ice crystals. It is noted that,while the rate of cooling is generally not a factor with regard to theformation of well defined, well-ordered, elongated fibers where thecooling is substantially unidirectional, the rate of cooling doesdefinitely affect the size and shape of the crystal. Rapid cooling ratesresult in the formation of minute, microscopic ice crystals. Slowercooling or freezing rates result in the formation of long, needle-likeice crystals. Preferred cooling rates, defined in terms of the rate ofadvance of the freezing boundary, range from about 0.02 to about 1.0ft/hr, more preferably from about 0.03 to about 0.5 ft/hr.

While there is nothing presently believed critical in the temperature ofthe protein solution or slurry prior to the freezing step, it isconsidered preferable to reduce the temperature of the solution orslurry to as close to the freezing point as possible prior to subjectingit to freezing. This is preferred at the present time solely on thebasis of economics. It is less expensive to cool a liquid byconventional means with turbulence and high surface contact with theheat transfer media than to cool by means of the single or two opposedheat transfer elements employed for freezing. It is cautioned, however,that the liquid mixture should not be supercooled prior to the freezingoperation as this will result in too rapid, random cooling and willproduce an undesirable, random fiber structure in the product.

Unexpectedly, when this frozen material is immersed in a liquid, such asliquid nitrogen, substantially colder than the frozen mass, cleavageplanes are produced perpendicular to the direction of fiber formation. Asimilar effect is noted when the frozen mass is immersed in asubstantially warmer liquid. After stabilizing the protein, and heatingas will be hereinafter discussed, the product can be rehydrated to givea surprisingly fish-like texture. While not wishing to be bound by anytheory, a plausible explanation of what is occurring during this processis based on the manner in which the material reacts during freezing.During the unidirectional freezing step, a concentration gradient of thedissolved solids (e.g. salts, aminoacids, polypeptides etc.) isgenerated along the fiber axis. This gradient occurs repeatedly as theice crystal front moves upward and away from the cooling surface. As aresult, planes of high and low solids concentration are generated alongthe fiber axis. Corresponding to these planes are weak regions (planes)perpendicular to the fiber axis. When the frozen material issubsequently immersed in a bath at a substantially warmer or coldertemperature, (e.g. liquid N₂), the expansion of the ice crystals alongthe fiber axis causes the fiber to crack along the weak planes therebygiving a structure similar to tuna fish muscle upon freeze-drying andheat setting. In the exemplary situation where the minimum dimension ofthe frozen mass is about two inches, the temperature during immersion ispreferably at least 50° C colder or warmer than the frozen mass, andmore preferably at least 100° C different. Where the minimum dimensionis greater, the temperature difference must also be greater; wherelesser, the temperature difference can be lesser.

After freezing, and shock temperature treating as described above, thecrystalline structure of the material can be easily observed, ifdesired, by fracturing the frozen mass and observing it visually. Toretain the integrity of the individual protein fibers thus formed, theprotein is stabilized according to the present invention by freezedrying as disclosed in said Ser. No. 480,987, or by immersing the frozenmass in an aqueous solution, comprising an edible, water-solublematerial capable of lowering the freezing point of water and stabilizingthe protein. If the substantially soluble protein is not stabilizedprior to heating, such as for heat setting, the heating will result inexcessive bonding of the individual fibers due to melting of the icecrystal lattice separating them. As the fibers are then heat set, theytend to form a less distinctly fibrous mass. For fish analogsespecially, this excessive bonding of the protein material is undesired.Also in this regard, the frozen mass should not be stored attemperatures which are only slightly below the freezing point of themass for extended periods of time. Storage under these conditions willcause recrystallization of the ice and randomization of the fibrousstructure. While this may be desirable to some extent as a means ofaffecting the texture of a final meat analog, it must only be done withthe knowledge that reorientation is occuring, and it must be allowed toproceed only to the extent that would be desirable for a particularapplication.

The frozen mass can be freeze dried in conventional manner usingconventional equipment. The product can be subdivided either before orafter freeze drying. It should be dried sufficiently to reduce themoisture content to the point where the structure does not collapse. Thedetails of freeze drying are well known to those skilled in the art andform no part of the present invention. A detailed discussion of freezedrying techniques which would be suitable according to the presentinvention reference is made to Van Arsdale, W.B., and Morgan, A.I.; FoodDehydration, Second ed., Vol. 1; AVI publishing. In an exemplary freezedrying situation a laboratory freeze dryer is employed to freeze a oneinch thick slab having a total volume of 3 liters. The drying takesapproximately two days to reduce the moisture content to a level of fromabout 3% to about 5%. In this specific set-up, the plate temperature isabout 20° to about 30° C, preferably about 25° C; the condensertemperature is from about -40° to about -70° C, preferably about -50° C;and the pressure of the freeze drying chamber is from about 20 to about50 microns, preferably from about 30 to about 40 microns, of Hg. Thisset of conditions is merely exemplary of those which can be employed andis not to be taken as limiting of the present invention. Any freezedrying technique which is capable of drying the fibers toself-sustaining form, preferably to a moisture content of less thanabout 10%, while not allowing substantial melting of the ice crystals toallow excessive bonding of the fibers and does not maintain thetemperature at too high a level for a period of time which would causerandomization of the fibrous structure, would be effective andappropriate according to the present invention.

Alternatively, the frozen mass can be immersed in a stabilizing solutionin any convenient manner using conventional equipment. The product canbe subdivided either before or after immersion. Water miscible organicsolvents have been previously used to precipitate proteins, and any ofthese known materials can be used as the stabilizing material in aqueoussolution so long as they decrease water availability to the protein,decrease the hydrophillic potential of the protein by causingconformational changes in the protein, lower the freezing point of thewater and lower the surface tension of the water. The amount of wateravailable to the protein is reduced simply by the reduced mole fractionof water in the presence of these stabilizing materials. Thus, the wateris less available for dissolving the protein. The effective stabilizingmaterials also enhance the displacement of the equilibria ##STR1## tothe right, thereby adversely affecting the solubility of the proteins.The most effective stabilizing materials which can be employed, reducethe surface tension of the water and thereby reduce the contribution ofthe water to protein hydrophobic group adherence. The most noticeabledeadherence effective in decreasing protein solubility is noticed, inthe case of organic solvents, where the molecules have short,straight-chained hydrophobic groups. Reducing the freezing point of thewater is essential because the stabilizing material must be able topenetrate the ice in the frozen product mass.

Among the suitable stabilizing materials are the polar organic solventssuch as alcohols, with ethanol and propanol being preferred on the basisof their lack of toxicity even where large residual amounts of thesesolvents remain in the product. Ethanol is particularly preferred;however, any solvent can be employed so long as it has the indicatedfunctionality and is not toxic at the reasonable levels which may remainin the product after removal of the solvent by known techniques such asextraction and drying. Also suitable as the stabilizing or coagulatingmaterials are the known acids and salts having the necessaryfunctionality in aqueous solution. If desired, these known salts and/oracids can be employed in combination with an alcohol, such as ethanol,or other organic solvent. Such combinations are desirable from thestandpoint that it allows a balancing of the benefits and liabilities ofthe various stabilizing agents for a particular processing or productapplication. Among the suitable acids are hydrochloric, sulphuric,phosphoric, acetic and other edible acids. Among the suitable salts arethe edible ammonium, alkali metal and alkaline earth salts of theseacids as well as other salts having the indicated functionality.

While only exemplary of suitable stabilizing materials which can beemployed, ethanol will be employed as the stabilizing material in thefollowing discussion for conciseness. When a frozen mass of protein andice prepared in the manner described above is brought into contact withethyl alcohol in a coagulation bath, a diffusional interchange occursbetween the two phases, water in the protein and the ice crystals, andethyl alcohol. The ice crystals melt and water leaves while alcoholenters the protein phase. As soon as protein comes into contact withalcohol, it is insolubilized and the fibers stabilized. In order toinsolubilize the protein completely, alcohol has to diffuse into theprotein phase thoroughly. After a sufficient length of time, no moreexchange takes place: hence, a state of equilibrium is achieved betweenthe two phases. The final equilibrium concentration of alcohol in thecoagulating bath is dependent on the ratio of alcohol to water in thefrozen protein mass. The concentration of alcohol in this coagulatingbath affects the freezing point of solution as well as the diffusionrate and coagulation rate of protein which are important factors tocontrol in this process.

When the unidirectionally frozen protein mass is immersed in the alcoholbath to stabilize the freeze-aligned fibrous structure, the temperatureof the bath must be lower than freezing point of the protein solution.This immobilizes free water and thereby minimizes rehydration of theprotein and dissolution of the freeze-aligned structure by water. At thefreezing temperature, water exists as ice crystals in the protein mass.When ice crystals contact with alcohol, the ice melts and water diffusesout; at the same time the protein also contacts with a sufficientconcentration of alcohol and is insolubilized. If the temperature ofalcohol bath is close to freezing point of water, higher than -5° C,recrystallization takes place in the frozen protein block, and theunidirectional fibrous structure disappears and a random structure isformed.

Freezing point depression is dependent on the concentration of soluteadded in solution. Therefore, the freezing point of coagulating bath canbe regulated by changing the concentration of alcohol. In order toprevent freezing the alcohol bath, the freezing point of coagulatingsolution must be lower than the processing temperature.

While any effective concentration of stabilizing material can beemployed, in the case of ethanol, it is found that the concentrationshould be maintained at above about 10%, and preferably above 20%. Withone particular sample using 5% ethanol, the protein was completelysolubilized and fibrous structure was disintegrated. At 10%, the proteinwas partially solubilized and fibers were very soft. However, the fibersdid not fall apart. At 20% alcohol, the protein was not solubilized. Thetexture was soft due to partial hydration. At higher than 30% alcohol,the protein was completely insoluble and the texture of the fibrousmaterial was hard. When the final equilibrium concentration of alcoholin this coagulation process was higher than 70%, the fibers were veryfragile due to excessive dehydration of protein. It appears that optimumconcentration at equilibrium was about 60% of ethyl alcohol.

Ethanol soluble pigments, carbohydrates, oil and fat in proteinmaterials are diffused out during this process. This is desirable fromthe standpoint of removing pigments and flatulents from the products.Fat and oil can be recovered and used in foods.

Once stabilized by freeze drying or immersion as described above, thefibrous mass can be dried, stored for indefinite periods of time andlater heat set; or heat set immediately and then stored for subsequentuse. It is possible through the proper selection of the particular typeof heat treatment, to effect the texture, color, toughness, tensilestrength, rehydration and water retention properties of the finalproduct. Textured materials receiving severe heat treatment tend toretain less water upon rehydration. However, all textured materialsaccording to the present invention preferably receive an amount of heattreatment sufficient to increase the structural integrity of the fibers.Materials receiving mild heat treatment tend to be softer and morepliable than those which receive severe heat treatment. Moist heattreatment is highly efficient and gives an extremely good meat-liketexture to the final product.

The amount of heat treatment, with or without pressure, to stabilize theproduct varies with the type of protein materials used. By way ofexample, dry soy milk fibers are preferably heat treated in an autoclaveunder a 15 psig pressure for from about 5 to 10 minutes to stabilize thestructure, and fibers from soy flour, on the other hand, are preferablyheat treated for from 20 to about 25 minutes under the same conditions.Any combination of time, temperature, and pressure effective to heat setthe protein into substantially independent fibers can be employedaccording to the present invention. It appears that heat treatment at atemperature ranging from about 100° to about 120° C for a time of fromabout 5 to about 30 minutes is adequate depending upon the texturedesired in the final product. The exact times, temperatures, andpressures employed will be easily determinable by those skilled in theart for a wide variety of products. Reference to the examples below willshow a number of specific heat treatment operations which will guidethose skilled in the art.

Typical of the heating means which can be employed are conventionalautoclave or steam chamber devices capable of producing pressures of upto about 20 psig and temperatures of up to about 130° C. Also suitablewould be electric or gas-fired infrared ovens capable of operating underconditions of high relative humidity. The use of moist heat in suchdevices, or in the autoclave or steam chambers previously mentioned,aids in providing a more complete coagulation or immobilization of theprotein materials. The specific heating means employed is not criticalto the present invention. All that is necessary is that the heat besufficient in time and intensity to coagulate or immobilize the proteinsufficiently to substantially prevent loss of the individual proteinfibers upon rehydration.

After heat setting, the fibrous protein material can be marketed as is,or rehydrated immediately to obtain a more meat-like texture. Theproduct is easily rehydrated by soaking in water for a period of timeeffective to obtain a desired water content. The rehydrating solutioncan contain acids for neutralizing any residual alkali, or flavorings,emulsified fats, flavor enhancers, condiments, sugars, heat coagulableor soluble proteins, amino acids, and the like. In this manner, theproduct can be modified to have the taste as well as the texture offish. Of course, as indicated previously, these ingredients can also beemployed in the aqueous protein mixture before freezing. Experience withparticular recipes will dictate at what point these additives areemployed.

The following examples are presented for the purpose of furtherexplaining and illustrating the present invention, and are not to betaken as limiting in any regard. Unless otherwise indicated, all partsand percentages are by weight.

EXAMPLE I

To prepare a texturized soy protein product having highly-oriented,well-defined fibers in a fish-like texture, a soy milk is used as aprotein source. The soy milk is prepared by soaking 600 grams of soybeans overnight in water, changing the water several times. The soakedbeans are then hot ground with boiling water, the water being present ata 10:1 ratio with regard to the soy beans. The resulting slurry isheated to boiling and held there for 15 minutes, and filtered through adouble layer of cheesecloth. The residue on the cheesecloth is discardedand the level of solids in the supernatant is determined. The pH of thesupernatant is then adjusted to 7.5 using 2N sodium hydroxide, and anantioxidant is added to the supernatant at a level equivalent to 0.02%of the fat content. Because full fat soy beans are employed, the fatcontent of the supernatant is about one-fourth the weight of the solidspresent. The soy bean milk is then placed in an aluminum pan to a depthof about one inch. The pan is placed on a block of dry ice (-76° C)which extends across the entire bottom surface of the pan.Unidirectional ice crystals, substantially perpendicular to the bottomof the pan, are generated. The mass is completely frozen in about 30minutes. The frozen mass is then placed in liquid nitrogen for about oneminute during which time this shock cooling causes planes of fracturestransverse to the direction of alignment of the fibers. The frozen massis removed from the pan and immersed in 95% ethanol at the weight ratioof 1:4 for 8 hours with stirring at a temperature ranging from -5° to-10° C. The stabilized fibrous material is pressed by applying forceperpendicular to the direction of fibers to hasten the release of ethylalcohol trapped in the spaces between the fibers. The pressed product isthen air dried to remove water and residual ethanol. This drying processstrengthens the structure. This dried material is autoclaved at 15 psigfor 10 minutes to strengthen the structure. The heat set material isthen rehydrated by soaking in water for about 20 minutes to yield aproduct having discrete, soft, chewy, fish-like fibers.

EXAMPLE II

To prepare a texturized soy protein product having highly-oriented,well-defined fibers in a fish-like texture, a soy milk is used as aprotein source. The soy milk is prepared by soaking 600 grams of soybeans overnight in water, changing the water several times. The soakedbeans are then hot ground with boiling water, the water being present ata 10:1 ratio with regard to the soy beans. The resulting slurry isheated to boiling and held there for 15 minutes, and filtered through adouble layer of chessecloth. The residue on the cheesecloth is discardedand the level of supernatant is then adjusted to 7.5 using 2N sodiumhydroxide, and an antioxidant is added to the supernatant at a levelequivalent to 0.02% of the fat content. Because full fat soy beans areemployed, the fat content of the supernatant is about one-fourth theweight of the solids present. The soy bean milk is then poured into atwo inch cellulose sausage casing to a height of about one foot. Thecasing is lowered in one-half inch intervals into a bath cooled to -40°C. The soy milk is allowed to freeze to a height of about 11/2 inchesabove the surface of the bath each time before further lowering thecasing until the ice-liquid interface is about 1 inch above the surfaceof the bath. Unidirectional ice crystals, substantially perpendicular tothe surface of the bath, are generated. Lowering the casing from the airabove the bath into the bath causes shock stressing of the mass andfracturing at planes of weakness due to the temperature differentialbetween the mass as maintained above and below the surface of the bath.The frozen mass is removed from the pan and immersed in 95% ethanol atthe weight ratio of 1:4 for 8 hours with stirring at a temperatureranging from -5° to -10° C. The stabilized fibrous material is pressedby applying force perpendicular to the direction of fibers to hasten therelease of ethyl alcohol trapped in the spaces between the fibers. Thepressed product is then air dried to remove water and residual ethanol.This drying process strengthens the structure. This dried material isautoclaved at 15 psig for 10 minutes to strengthen the structure. Theheat set material is then rehydrated by soaking in water for about 20minutes to yield a product having discrete, soft, chewy, fish-likefibers.

EXAMPLE III

The procedure of Example II is repeated, but this time the material isfreeze dried instead of immersing it in the ethanol. The freeze driedmaterial is then treated with moist heat at 15 psig for 10 minutes tostabilize the structure.

EXAMPLE IV

A fibrous soy protein product is prepared from soy protein isolate. Here100g of soy protein isolate (91% protein) was mixed with 900g of waterto make 10% solution and pH was adjusted to 7.0-8.0. This solution isplaced in a pan to a depth of about 1 inch and frozen and stabilized asdescribed in Example I.

EXAMPLE V

A fibrous peanut protein product is prepared from peanut proteinisolate. Here 150g of peanut protein isolate (93% protein) was mixedwith 850g of water to make 15% solution and pH was adjusted to 7.0-8.0.This solution is placed in a pan to a depth of about 1 inch and frozenand stabilized as described in Example III.

EXAMPLE VI

A fibrous egg albumin product is prepared from fresh egg white. Thewhites of several eggs are separated from the yolks, placed in a pan,frozen and stabilized as described in Example I. Here 10% egg albuminsolution prepared from egg white powder can be successfully used.

EXAMPLE VII

A fibrous fish protein product is prepared from a 15% aqueous mixture offresh fish meat. To prepare the aqueous mixture, 150g of lean fish meatis homogenized with 850 ml of cold 3% Nacl aqueous solution in a WaringBlendor at high speed for about 5 minutes under vacuum. The resultinghomogenate mixture is then placed in a pan, frozen, and stabilized asdescribed in Example III.

EXAMPLE VIII

The procedure of Example I is again repeated, but this time the soybeanmilk is concentrated as follows: The pH of the soybean milk is adjustedto 4.5 by adding HCl (1N). The resulting precipitate is separated bycentrifugation at 5,000 × G for 20 minutes. The supernatant isdiscarded. The precipitate is transferred to a mixer and mixed withwater for 20 minutes to get a smooth and concentrated (18 to 20% solids)soybean milk. The soybean milk slurry is then adjusted to a pH of about7.5 using 2N sodium hydroxide and the resulting solution is placed in apan, frozen and further processed as in Example I.

Many modifications and variations of the present invention will beapparent to those skilled in the art upon reading the above disclosure.It is intended that all such modifications and variations be includedwithin the scope of the present invention which is defined by thefollowing claims.

What is claimed is:
 1. A method for preparing a texturized proteinmaterial comprising:(a) preparing a mixture comprising heat coagulableprotein and water; (b) cooling the mixture to freeze the water intoelongated ice crystals and to separate the protein into well-defined,well-ordered, substantially independent zones; (c) subjecting the frozenmass to a temperature at least 50° C different from that of the frozenmass to cause shock fracturing of the material at lines of weakness inthe frozen mass perpendicular to the elongated ice crystals; (d)stabilizing the protein in the frozen mass effectively to prevent lossof fibrous structure upon subsequent heating; and (e) heating thestabilized material to coagulate the protein.
 2. A method according toclaim 1 wherein the protein is stabilized by freeze drying.
 3. A methodaccording to claim 1 wherein the protein in the frozen mass isstabilized by immersing the frozen mass into an aqueous solution,comprising an edible, water-soluble material capable of lowering thefreezing point of water and stabilizing the protein, for a timeeffective to stabilize the protein in the frozen mass.
 4. A methodaccording to claim 3 wherein the edible water soluble material capableof lowering the freezing point of water and stabilizing the proteincomprises a member selected from the group consisting of ethanol andpropanol.
 5. A method according to claim 4 wherein the edible watersoluble material capable of lowering the freezing point of water andstabilizing the protein comprises ethanol.
 6. A method according toclaim 5 wherein the ethanol is employed in the aqueous solution at aconcentration of greater than 20% based on the weight of solution priorto immersion of the frozen mass therein.
 7. A method according to claim6 wherein the stabilized protein is treated to remove residual ethanol.8. A method according to claim 7 wherein the residual ethanol is removedby subjecting the stabilized protein to a vacuum.
 9. A method accordingto claim 1 wherein the pH of the mixture comprising protein and water isadjusted to increase the solubility of the protein.
 10. A methodaccording to claim 1 wherein the temperature of step (c) is at least 50°C below that of the frozen mass.